1. Field of the Invention
The present invention relates to a phase shift mask for use in the exposure and transfer of a fine pattern and a phase shift mask blank or the like as its parent material. More particularly, the present invention relates to a halftone phase shift mask and a halftone phase shift mask blank or the like.
2. Description of the Related Art
In the art of DRAM (Dynamic Random Access Memory), the trend toward high integration beginning with 1 Mbit has gone so far as to establish a system for the mass production of 64 Mbit and 256 Mbit DRAM""s at present. This technological innovation witnessed a tendency toward the use of ultrahigh voltage mercury vapor lamp emitting light having a shorter wavelength, i.e., i-ray (365 nm) instead of g-ray (436 nm), as an exposing light source. The reduction of the wavelength of exposing light is being still considered for further integration. In ordinary photolithographic process, however, the reduction of the wavelength of exposing light causes the reduction of the depth of a focus while improving the resolution. This not only increases the burden on the design of the exposing light system but also remarkably deteriorates the stability of the process, giving an adverse effect on the yield of the product.
A phase shift process is one of ultrahigh resolution pattern transfer processes effective for the solution to the foregoing problems. In the phase shift process, as a mask for use in the transfer of a fine pattern there is used a phase shift mask.
A phase shift mask comprises, e.g., a phase shifter portion having a pattern portion formed on the mask and a non-pattern portion (exposed portion of the substrate) free of phase shifter. The phase of light transmitted by the two portions are shifted by about 180xc2x0 so that the two light components interfere with each other at the pattern interface to exert an effect of enhancing the contrast of the transferred image. Further, the use of the phase shift process makes it possible to increase the depth of a focus for the necessary resolution. Accordingly, the enhancement of resolution and the expansion of applicability of process can be accomplished at the same time even if light having the same wavelength is used as compared with the conventional transfer process using an ordinary mask having an ordinary light-shielding pattern made of chromium film or the like.
Practically speaking, phase shift masks can be roughly divided into two groups, i.e., completely transparent type (Shibuya-Revenson type) phase shift mask and halftone phase shift mask. In the former type of phase shift mask, the light transmittance of the phase shifter portion is the same as that of the non-pattern portion (exposed portion of the substrate). This mask is almost transparent to the wavelength of the exposing light and thus is generally said to be effective for the transfer of a line-and-space pattern. On the other hand, in the latter type of phase shift mask, the light transmittance of the phase shifter portion is from several percents to scores of percents of that of the non-pattern portion (exposed portion of the substrate). This phase shift mask is said to be effective for the preparation of contact hole or lone pattern in the process for the production of semiconductors.
FIG. 1 is a diagram illustrating the basic structure of a halftone phase shift mask blank. FIG. 2 is a diagram illustrating the basic structure of a halftone phase shift mask. The description of anti-reflection layer or etching stop layer which may be used in lithographic process will be omitted.
The halftone phase shift mask blank comprises a semitransparent film (halftone phase shifter layer) 2 formed on a transparent substrate 1. The halftone phase shift mask comprises a phase shifter portion 3 having a pattern portion formed on the mask and a non-pattern portion (exposed portion of the substrate) 4 free of phase shifter. The phase shifter portion 3 acts as a phase shifter capable of shifting the phase of exposing light transmitted by the neighborhood of its edge while being capable of substantially shielding the exposing light from the resist formed on the substrate.
Among these halftone phase shift masks is a single layer-type halftone phase shift mask which is simple enough in structure to produce. Examples of such a single layer-type halftone phase shift mask include those having a phase shifter made of a chromium material such as CrOx, CrN, CrOxNy and CrxONyC2 as described in JP-A-5-127361 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), those having a phase shifter made of an MoSi material such as MoSiO and MoSiON as described in JP-A-6-332152, and those having a phase shifter made of an SiN or SiO material as described in JP-A-7-261370.
The recent years have witnessed the reduction of the wavelength of exposing light used in the art as well as the trend for more use of halftone phase shift mask. There has recently been a tendency toward the use of krypton fluoride (KrF) exima laser beam (248 nm), which has a wavelength shorter than i-ray. Further, the use of argon fluoride (ArF) exima laser beam (193 nm) or argon chloride (ArCl) exima laser beam (175 nm), which has a wavelength even shorter than i-ray, has been proposed.
With the reduction of the wavelength of exposing light, the corresponding phase shift mask and phase shift mask blank must meet an important requirement, i.e., control over optical coefficients such as transmittance and refractive index in the wavelength of exposing light used. Most substances show remarkably great light absorption in a wavelength range shorter than 250 nm unlike in the wavelength range of from visible light to near ultraviolet. Thus, it is difficult to control the light transmittance of substances to a desired value in this short wavelength range. Thus, a halftone phase shift mask for i-ray cannot be normally used as a halftone phase shift mask for the exposing light having a wavelength range shorter than 250 nm as it is. Referring to the predetermination of the transmittance of the halftone type phase shifter, it is preferred that the transmittance of exposing light can be controlled to a range of from 3 to 20% when the phase shifter has a thickness at which the phase of exposing light can be shifted by a predetermined angle in the case of halftone phase shift mask, though depending on the sensitivity of the resist to be used in the transfer of a pattern or the patterning process.
Another problem is that even if the foregoing basic requirements such as transmittance and refractive index in the wavelength of exposing light can be satisfied to cope with the reduction of the wavelength of exposing light, the transmittance, if it is high with respect to the wavelength of testing light (e.g., 364 nm, 488 nm, 633 nm), cannot be examined, making it impossible to put the mask into practical use. Therefore, it is required that the transmittance of the mask with respect to the wavelength of testing light can be controlled to a desired value to put the mask into practical use.
Further, a halftone phase shift mask and a halftone phase shift mask blank as a parent material from which it is prepared must satisfy some requirements besides the foregoing requirements, i.e., inertness to irradiation with exima laser used (light resistance), chemical durability at cleaning process indispensable for mask process (chemical resistance), minimization of microdefects in the blank that remarkably deteriorate the mask quality (low defect density).
More particularly, the reduction of the wavelength of exposing light is also accompanied by the increase in the density of energy applied per unit time. In this respect, the layer material from which the phase shifter layer is formed must satisfy requirements that it doesn""t impair the function of phase shift mask even when damaged by irradiation with light of higher energy. The term xe2x80x9cdamagexe2x80x9d as used herein is meant to indicate change in optical properties (e.g., refractive index, transmittance) of shifter layer, occurrence of color defects, change in layer thickness or deterioration of layer properties by irradiation with light. It is said that when irradiated with exima laser beam having a wavelength in the deep ultraviolet range, the phase shifter layer undergoes two-photon process that excites substances therein, leading to change in the optical properties or other properties of the layer. However, the detail of the mechanism is not yet made clear. Anyway, it is an indispensable condition that the phase shifter layer has a high resistance to irradiation with a high-energy light to cope with the reduction of the wavelength of exposing light.
Taking into account the material of the shifter layer from the standpoint of mask material, the shifter layer must not undergo denaturation or dissolution when cleaned with an acid or alkali at the process for the preparation of mask. In other words, the phase shifter layer must be chemically durable regardless of the wavelength of exposing light.
Further, from the standpoint of the fact that a phase shift mask is a tool for fine work, the halftone phase shift mask blank needs to be workable to a higher precision (e.g., patterning, etching). To this end, the phase shifter layer must be homogeneous and free of defects. It is said that the reduction of the wavelength of exposing light will be accompanied by further rise in the fineness of mask pattern. Thus, defects in the phase shifter layer cause an important problem which governs the reliability of the transfer of pattern.
However, the conventional process for the production of a halftone phase shift mask blank is disadvantageous in that since the satisfaction of the foregoing requirements, if needed to be accomplished by controlling the content of oxygen, nitrogen, etc. in an MSi semitransparent film (M is a metal or transition metal element), is normally accomplished by the employment of a process involving the control over the content of oxygen, nitrogen, etc. in the sputtering gas (i.e., flow ratio in sputtering gas), the required properties can hardly be closely controlled.
In particular, plasma discharge process with oxygen gas (reactive sputtering process) is often liable to abnormal discharge due to insulating oxide formed on the surface of the target. Abnormal discharge occurs on the surface of the target to cause finely divided particles to be scattered. These particles are then taken into the semitransparent film where they act as defects to remarkably deteriorate the quality of the semitransparent film (halftone phase shifter).
Further, the content of oxygen, nitrogen, etc. in the semitransparent film can hardly be closely controlled by adjusting the flow ratio of the sputtering gas. For example, in order to obtain a desired transmittance with an SiN layer, it is necessary that the content of nitrogen be accurately controlled within a narrow range. However, this operation can hardly be effected. Further, this operation has a poor reproducibility.
The present invention has been worked out under the foregoing circumstances. It is therefore an object of the present invention to provide a process for the production of a halftone phase shift mask blank which enables the accurate and easy control over the composition of an MSi semitransparent film that makes it easy to obtain an MSi semitransparent film having a desired specific component, the formation of film with ease at a good reproducibility and the reduction of defects in the layer.
The foregoing object of the present invention will become more apparent from the following detailed description and examples.
The foregoing object of the present invention is accomplished by the following constitutions.
(Constitution 1) A process for the production of a halftone type phase shift mask blank adapted for the preparation of a phase shift mask having a semitransparent film formed on a transparent substrate, said semitransparent film being capable of making the phase of light transmitted through said semitransparent film different from that of light transmitted directly through said transparent substrate by a predetermined amount and reducing the intensity of light transmitted through semitransparent film, characterized in that said semitransparent film is formed using a sputtering target comprising at least one element selected from the group consisting of metal elements and transition metal elements, silicon and at least one compound selected from the group consisting of oxide, nitride and oxinitride of these elements.
(Constitution 2) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said sputtering target comprises nickel, silicon and at least one compound selected from the group consisting of oxide, nitride and oxinitride of these elements.
(Constitution 3) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said sputtering target comprises at least one element selected from the group consisting of metal elements and transition metal elements, nickel, silicon and at least one compound selected from the group consisting of oxide, nitride and oxinitride of these elements.
(Constitution 4) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said sputtering target comprises at least one element selected from the group consisting of metal elements and transition metal elements, silicon, aluminum and at least one compound selected from the group consisting of oxide, nitride and oxinitride of these elements.
(Constitution 5) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said sputtering target comprises at least one element selected from the group consisting of metal elements and transition metal elements, nickel, silicon, aluminum and at least one compound selected from the group consisting of oxide, nitride and oxinitride of these elements.
(Constitution 6) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said metal element or transition metal element is at least one element selected from the group consisting of molybdenum, chromium, tungsten, tantalum, cobalt, vanadium, palladium, titanium, niobium, zinc, zirconium, hafnium, germanium, platinum, manganese and iron.
(Constitution 7) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said semitransparent film is formed using a mixture of a gas containing at least one element selected from the group consisting of nitrogen, hydrogen and oxygen and an inert gas as a sputtering gas.
(Constitution 8) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein said sputtering target used has a substantial oxygen content of from 0 to 70 atm % and a substantial nitrogen content of from 0 to 65 atm % and said semitransparent film prepared using said target has an oxygen content of from 0 to 65 atm % and a nitrogen content of from 0 to 60 atm %.
(Constitution 9) The process for the production of a halftone phase shift mask blank according to Constitution 1, wherein the type of discharge to be applied to said sputtering target to produce plasma is any of dc, ac having a frequency of not more than 500 KHz and high frequency wave having a frequency of 13.56 MHz.
(Constitution 10) A process for the production of a halftone phase shift mask, which comprises forming a semitransparent mask pattern to be transferred to a wafer on a transparent substrate using a halftone phase shift mask blank prepared by the process defined in Constitution 1.
(Constitution 11) A process for the production of a halftone phase shift mask, which comprises subjecting a semitransparent film formed on a transparent substrate by the process defined in Constitution 1 to dry etching with a gas containing chlorine and/or gas containing fluorine.
(Constitution 12) A halftone phase shift mask prepared by the process defined in Constitution 10, characterized in that a phase shifter made of said semitransparent film is designed to have a transmittance of from 3 to 20% with respect to desired exposing light having a wavelength of from 150 nm to 370 nm and act as a phase shift mask.
(Constitution 13) A process for the transfer of a pattern, which comprises transferring a pattern using a halftone phase shift mask defined in Constitution 12.
(Constitution 14) The method of manufacturing a halftone phase shift mask blank according to Constitution 1, wherein said sputtering target comprises at least one compound selected from the group consisting of oxide and oxinitride of at least one element selected from the group consisting of metal elements and transition metal elements.
(Constitution 15) The method of manufacturing a halftone phase shift mask blank according to Constitution 14, wherein said sputtering target further comprises at least one compound selected from the group consisting of oxide and oxinitride of silicon.
In accordance with Constitution 1, a process involving the introduction of oxygen and nitrogen into the semitransparent film from the target which has previously comprised oxygen and nitrogen in the form of oxide, nitride and oxinitride of M (M is a metal or transition metal element) or silicon incorporated therein makes it possible to efficiently take oxygen or nitrogen into the layer as compared with the conventional process involving the control over the flow ratio of sputtering gas such as oxygen and nitrogen. Thus, the composition of the semitransparent film can be accurately and easily controlled, making it possible to accurately and easily control the desired properties of the semitransparent film (easily adjust the properties of the semitransparent film to desired values). Further, this process makes it possible to form a film easily at a good reproducibility.
In particular, the foregoing process involves the previous incorporation of oxide in the target that eliminates the necessity of excessive introduction of oxygen as a sputtering gas, making it possible to avoid abnormal discharge and reduce defects in the layer.
Further, the incorporation of silicon in the target makes it practical to prepare an MSi target. In the case, sense silicon act as a binder in the target, it is able to prepare the target practically by sintering, CIP(Cold Isostatic Press) +sintering, or HIP( Hot Isostatic Press). This also makes it easy to prepare an MSi target having a specific composition.
The use of the MSi target having a specific composition makes it possible to prepare a semitransparent film which can satisfy basic requirements such as transmittance and refractive index with respect to the wavelength of exposing light as well as other requirements such as transmittance with respect to the wavelength of exposing light, light resistance, chemical durability (chemical resistance) and low defect density.
In accordance with Constitution 2, as opposed to the problem that an Nixe2x80x94Si target having a great Ni content, particularly with a specific component, can hardly be prepared, the incorporation of oxygen and nitrogen in the target makes it easy to prepare an Nixe2x80x94Si target having a specific composition (NiSiO, NiSiN, NiSiON, etc.). A semitransparent film having a specific component prepared using this target having a specific component can satisfy all the foregoing requirements.
In particular, an Nixe2x80x94Si semitransparent film having a specific composition (NiSiO, NiSiN, NiSiON, etc.) exhibits an excellent controllability over transmittance with respect to the wavelength of testing light. In some detail, a semitransparent film (NiSiO, NiSiN, NiSiON, etc.) having a desired transmittance or refractive index with respect to the wavelength of exposing light (248 nm, 193 nm, etc.) and a desired transmittance with respect to a desired testing light having a wavelength falling within the wavelength range of from 190 nm to 650 nm of testing light can be easily obtained.
In accordance with Constitution 3, the incorporation of M (metal or transition metal element) in the target, in addition to the effect of Constitution 2, allows the metal or transition metal element to act as a binder in the target, making it easy to prepare an Nixe2x80x94Si target having a specific composition.
Also in accordance with Constitution 3, the incorporation of a metal element and/or transition metal element in the target makes it easy to control and improve the required properties.
In accordance with Constitution 4, the following effect can be exerted in addition to the effects of Constitutions 1 and 3. In other words, aluminum acts similarly to silicon. However, oxides, nitrides and oxinitrides of aluminum can attain a relatively higher refractive index than oxides, nitrides and oxinitrides of silicon. Accordingly, the presence of silicon and aluminum in admixture makes it easy to change the optical coefficients of the phase shift mask and provides a wider control over the optical properties, making it possible to realize desired optical properties.
In accordance with Constitution 5, the effects of Constitutions 2 to 4 can be exerted at the same time.
In accordance with Constitution 6, the use of nickel, silicon and aluminum as the metal element and/or transition metal element M, in addition to the effect of Constitution 1, 3 or 4, not only makes it possible to attain the desired optical properties but also is effective for the enhancement of the electrical properties, optical properties and chemical durability of the layer. In some detail, the electrical properties which can be improved include the electrical conductivity of the layer. The optical properties which can be improved include the controllability over transmittance with respect to the wavelength of exposing light and the transmittance in the wavelength range of testing light for the mask. The chemical durability which can be improved include resistance to the acid or alkali used at the step of cleaning the mask.
In accordance with Constitution 7, the use of a gas containing at least one element selected from the group consisting of nitrogen, hydrogen and oxygen as a sputtering gas, in addition to the use of the target defined in Constitutions 1 to 6, provides a wider control over the required properties, making it possible to further improve the required properties.
In accordance with Constitution 8, if the substantial content of oxygen in the target exceeds 70 atm %, the content of oxygen in the resulting semitransparent film is excessive. If the substantial content of nitrogen in the target exceeds 65 atm %, the content of nitrogen in the resulting semitransparent film is excessive. Further, if the content of oxygen in the semitransparent film exceeds 65%, the transmittance all over the wavelength range rises, making it difficult to examine the layer. In addition, the resistivity of the layer rises or the refractive index of the layer decreases, making it impossible to satisfy the requirements for electrical and optical properties. Moreover, if the content of nitrogen in the semitransparent film exceeds 60 atm %, the transmittance all over the wavelength range rises, making it difficult to examine the layer, as in the oxygen content. In addition, the electrical and optical properties of the layer are deteriorated.
In Constitution 9, a desirable plasma discharge process suitable for the process of the present invention is defined.
In accordance with Constitution 10, the patterning of a blank obtained according to the process of the present invention makes it possible to obtain-a halftone phase shift mask which can satisfy all the requirements.
In accordance with Constitution 11, the combination of a semitransparent film obtained according to the process of the present invention and a dry etching process using a gas containing chlorine and/or a gas containing fluorine makes it possible to attain an excellent precision in fine work.
In accordance with Constitution 12, a halftone phase shift mask having desired optical and other properties can be obtained. In particular, a halftone phase shift mask having desired optical and other properties with respect to exposing light such as krypton fluoride (KrF) exima laser beam (248 nm), argon fluoride (ArF) exima laser beam (193 nm) and argon chloride (ArCl) exima laser beam (175 nm) can be obtained. In accordance with Constitution 13, the transfer of a pattern using a halftone phase shift mask according to the present invention makes it possible to realize a transfer process which can cope with the use of exposing light having a reduced wavelength.